‘PDF Merge’ is a very simple tool that lets you merge PDF documents with ease. Since it requires ‘.NET Framework 4’ to run, it should work natively in Windows 8 (as it comes with ‘.Net 4’ installed by default) and according to the developer, it also works on Windows 7 too.
It is an open source tool (GPL licensed) & other than merging the PDFs, it also lets you scan a document (from its windows) and then add it as a PDF file, change the order of the added PDF files, shows their sizes, names, pages, location and opens the merged PDF file automatically.
It is a very new application which is still at its ‘Beta’ stage, yet it worked pretty well in Windows 8. Its window however does not support resizing. It is not a big issue, but the default size of the main window feels like a bit bigger, so hopefully, that will be ‘fixed’ in the future releases.
Also, other than using the provided button, you can drag ‘n’ drop the file for adding to the list & before adding a scanned image, you can rotate them as well.
If interested, then please download it from this ‘CodePlex’ page.